Something is not right. All the Omega's i've seen (including mine) shoot at least 1.5MOA and in many cases even less (with sabots).
Powerbelts were horrible for me as far as accuracy. IMO, they simply are too loose in the barrel, and as such, im sure pressure escapes around the loose bottom. Sabots are tight, yes, but that what you need to maintain accuracy. I use the Prescision Rifle sabots, and they shoot .8MOA with Hornady 250gr .45 XTP bullets. I firmly believe a tight seal is essential for accuracy.
Do you swab between each and every shot? Here's my routine for using 777. First shot of the day from a clean barrel, no lube. After the shot, I swab the barrel with a wet patch (Number 13 solvent), turn the patch around, swab again, then follow up with a dry patch. In my experience, this cleans the barrel to almost like it was before the first shot. After a few shots, I may have to go back and forth on the crud ring to make sure it is dissolved. I can usually fire no more than two shots between cleanings if need be.
Claening between shots is essential. Once you have your stuff set up, firing off a round per minute is entirely possible. In the field, I don't bother carrying around the whole possibles bag worth of stuff. I simply carry a speed loader or three, with a patch or two in the powder compartment. I also carry the brass extender jag, and maybe a bullet starter. I use saliva as the cleaning lube. It has worked well so far, though after shooting a big buck, I found my mouth to be a little dry and it took a while to lube the patch!